th may 2019, devex · relative permeability is a major uncertainty in reservoir simulation tendency...

7th May 2019, DEVEX

TONY PETERS

The Water-Oil Ratio (WOR)

WOR vs. Fractional Flow

WOR Decline Curve Analysis

WOR & Relative Permeability

WOR & IOR

WOR & Simulation Forecasting QC

WOR & Allocation

WOR & Redevelopment

OUTLINE

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• Simple Analytical Tool

• Waterflood Developments (aquifer influx, water injection)

• WOR Plotlog WOR vs Cumulative Oil

• Standard Conditions

THE WATER-OIL RATIO (WOR)

𝑊𝑎𝑡𝑒𝑟 𝑂𝑖𝑙 𝑅𝑎𝑡𝑖𝑜(𝑊𝑂𝑅) =𝑊𝑎𝑡𝑒𝑟 𝑅𝑎𝑡𝑒 𝑏/𝑑

𝑂𝑖𝑙 𝑅𝑎𝑡𝑒 𝑏/𝑑

WOR Plot Key Components

• Post water breakthrough

• Initial rapid build – near well cone/cusp

• Turnover

• Post Turnover Trend

• to ultimate waterflood technical recovery for

development scheme (nominal, WOR100, 99%

w/c

• What happens post WOR not considered here

Scale Well, block, field, pipeline, basin, country

Reservoirs Majority – e.g. SS, chalk, fractured

Fluids All API’s so far developed in UKCS1

(Oil decline often flattens at high watercuts if liquid rates maintained to CoP)

4

2

2

3

3

4

1

5

5

Remaining mobile Oil @CoP

“SORW”

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WOR – THE UPTURN

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General perception that the WOR upturns at higher watercuts

Observation from simulation

Caused by simulation model boundary effects

Remove boundary effects, no upturn

Observed field upturns due to changes in reservoir hydrodynamic tilt (sweep).

e.g. reduced water injection, new offtake, etc.

PRESENTATION BASED ON DATA IN PUBLIC DOMAIN

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Sourcehttps://data-ogauthority.opendata.arcgis.com/datasets/oga-field-production-points-pprs-wgs84*

* Data from some fields incomplete

Water-drive fields with

No gas injection (or no post turnover GI)

Wells allowed to produce with developing watercuts

Steady GOR

Recovery extrapolation <Mobile OIP

CANDIDATE FIELDS FOR WOR

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Period of Post WBT

Optimization

E.G. BRENT PROVINCE*

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Waterflood & aquifers (small)

Similar fluids

Platform & subsea

Multiple operators

Actively managed

<15% Recovery Dry

Similar WOR

*https://www.spe-uk.org/aberdeen/wp-content/uploads/2014/10/SPE-Simplified-Series-2014-11-01-Maximising-Waterflood-Recovery-Tony-Peters1.pdf

NON IDEAL CANDIDATES

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Water & Gas Injection

Aquifer +Gas Cap

Active produced water management

Still suitable for selective application of WOR techniques• Well• Time

WOR VS. FRACTIONAL FLOW

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WOR+ Extrapolates from lower recovery+ No knowledge of fluid properties required

WOR DECLINE CURVE ANALYSIS

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Waterflood DCA key inputs for waterflood Fields• Liquid rate • Watercut development

WOR based DCA - Ideal for fields with fluctuating production histories Oil & Water Forecasts

E.G.

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Workflow• Choose WOR Match Period• Generate exponential type curve of WOR vs Cum Oil



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Workflow• Choose WOR Match Period• Generate exponential type curve of WOR vs Cum Oil• Calculate Oil Rate

𝑂𝑖𝑙 𝑅𝑎𝑡𝑒 𝑏/𝑑 =𝐿𝑖𝑞𝑢𝑖𝑑 𝑅𝑎𝑡𝑒 𝑟𝑏/𝑑

(𝑊𝑎𝑡𝑒𝑟 𝑂𝑖𝑙 𝑅𝑎𝑡𝑖𝑜 ∗ 𝐵𝑤) + 𝐵𝑜

Bw – Water FVF rb/bblBo – Oil FVF rb/bbl


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Workflow• Choose WOR Match Period• Generate exponential type curve of WOR vs Cum Oil• Calculate Oil Rate • Calculate Water Rate

𝑊𝑎𝑡𝑒𝑟 𝑅𝑎𝑡𝑒 𝑏/𝑑 = 𝑊𝑂𝑅 ∗ 𝑂𝑖𝑙 𝑅𝑎𝑡𝑒 𝑏/𝑑


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Workflow• Choose WOR Match Period• Generate exponential type curve of WOR vs Cum Oil• Calculate Oil Rate • Calculate Water Rate• Repeat for DCA cum oil anchored at start of WOR match period



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Workflow• Choose WOR Match Period• Generate exponential type curve of WOR vs Cum Oil• Calculate Oil from • Calculate Water from• Repeat for DCA cum oil anchored at start of WOR match period• Assess match quality • Refine


WOR DECLINE CURVE ANLYSIS

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Workflow• Choose WOR Match Period• Generate exponential type curve of WOR vs Cum Oil• Calculate oil from • Calculate water from• Repeat for DCA cum oil anchored at start of WOR match period• Assess match quality • Refine• Forecast vs. liquid rate

• Compare forecasts with simulation model – informs whether simulation model is optimistic or pessimistic


Qo Forecast – low liquid rate

Qo Forecast – high liquid rate

Qw Forecast – high liquid rate

Qw Forecast – low liquid rate


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Example #2Quieter WORDeclining Liquid Rate


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Example#3

Whole Production History

DCA on Cone/Cusp

WOR Production Type Curve

WOR reflects field scale relative permeability

Captures impact of reservoir heterogeneity, gravity, Pc, wettability, on recovery efficiency

Relative permeability is a major uncertainty in reservoir simulation

Tendency to adjust relative permeability to achieve history match with a geological realization

Relative permeability can be generated from observed WOR

Allows reservoir engineer to fix relative permeability @start of history matching process.

Enhances history matching workflow, improves quality of forecasts.

WOR & RELATIVE PERMEABILITY

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Workflow – Spreadsheet Work

Fractional Flow (FW) & WOR generated from all production data

FW forecast from post turnover WOR extrapolation

FW post WOR turnover matched with corey curve – to 100% FW

Doesn’t match Pre WOR turnover FW

FW Pre WOR turnover matched on trial and error basis

Relative Permeability Curve Suitable to Forecast to 100% watercut

RELATIVE PERMABILITY FROM WOR

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Corey Match

T&E

1

3

3

2

1

2

Corey Match

T&E

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WOR – RELATIVE PERMEABILITY

Fine Grid Rel. Perm = 119 x 21 x 7

VS.

Coarse Grid Pseudo = 17 x 3 x 1

Fine Scale

Coarse with Corey Curve

Match to WOR Turnover

period only

Coarse, Corey +

T&E

• Match achieved first time with WOR generated pseudo relative permeability

A rel perm with excellent predictive capability

Utility in Material Balance/Integrated Production Models

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WOR – RELATIVE PERMEABILITYAPPLIED TO FULL FIELD MODEL

Extrapolation from v low FW

Excellent match– first time

Careful selection of WOR extrapolation period

WOR & IOR

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WOR Excellent@• Identifying changes in reservoir performance• Quantifying net impact of changes

E.G.Discernible change in WOR character at end of match Period. Coincides with:

• 1st 4D Seismic• 1St Horizontal Well

For observed liquid can calculate deltas

Approach suitable for any changes (+/-)

(WOR vs time often used for surveillance)

WOR & SIMULATION FORECAST QC

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WOR plot a good reality check vs simulation model forecasts

E.G.Injector –producer pair, 100% VR200 md, varying KVKH

KV/KH1

0.10

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KV/KH1

0.10


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KV/KH1

0.10


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KV/KH1

0.10


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• Closer Look

WOR • Too flat, model optimistic past 70% watercut• Total Recovery > Mobile oil below top

perforation• Well draining more oil than it should

Subtle• Such artefacts difficult to eliminate• Can have significant impact on conclusions

re infill prospectivity

History Match with the DCA Forecast

WOR & SIMULATION FORECAST QCPROSPECT INTEGRITY

DATES01 SEP 2030 /

/WCONHIST‘P1' OPEN ORAT 500 5000 4* //

LTROWCONHIST+WCONPROD

e.g. – Two fields, shared flowline

WOR in each field changed

Production Performance ?

Reservoir Performance ?

Steady Pipeline (Meter ?) Level WOR

Potential allocation Issue

WOR DCA approach can help fill in the in the gaps in well test information

WOR & ALLOCATION

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WOR & REDEVELOPMENT

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• WOR plot can quantify the minimum amount of mobile oil left at CoP for development scheme• Volumes can be significant for large fields

Remaining mobile Oil @CoP

“SORW”

WOR & REDEVELOPMENT

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• A number of fields have been redeveloped

• Partially resaturation

• Observation• Production trends back to historic WOR

trend

WOR can be a useful tool for redevelopment option screening

WOR & DEVELOPMENT SIZING

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• Erratic Liquid Production History• 100 MMbbls+ Mobile oil at CoP

E.G.

WOR & DEVELOPMENT SIZING

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• WOR DCA Forecasts vs Assumed Liquid Rate• Reserves profile (etc.) vs. redevelopment option

• Conservative • Resaturation not accounted for• No optimization• Compare with simulation results - when/if available• No account of modern technology

• ICV, HW, 4D, designer water

• Workflow Suitable @ all Levels• well , common drainage, field, licence, HUB etc

Define ultimate recovery early in field life for active development scheme O/W/G Profiles, quantification of target volumes for IOR schemes

Quantify net recovery benefits of changes to base

Improve simulation & integrated production models

Reality check simulation forecasts

Improve confidence in simulation model predictions – base + infill potential

Improve allocation

Quantify minimum amount of mobile oil remaining at CoP and generate conservative objective profiles for redevelopment option screening

All from production data

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“PROBABLY THE BEST RESERVOIR ENGINEERING TOOL IN THE WORLD”

WOR SUMMARY

Thank You !

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th may 2019, devex · relative permeability is a major uncertainty in reservoir simulation tendency...

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